This invention relates to an engine and belt drive arrangement for a mower vehicle and more particularly to the arrangement of a belt drive for transferring power from the engine to the mower deck of a riding lawn mower. A belt drive arrangement for communicating power between an engine and a mower deck is known by those skilled in the art as a “mule drive”. A riding lawn mower may be considered in relation to an axis system including a longitudinal X axis where the positive direction is forward, a transverse Y axis where the positive direction is toward the operator's right and a Z axis where the positive direction is up. The X and Z axes define a vertical, longitudinal plane which generally bisects the riding lawn mower. Typically, a mule drive includes a drive sheave having an axis of rotation which is generally horizontal and co-planer with or at least parallel to the longitudinal plane of the mower vehicle. In a typical prior art mule drive, an endless belt communicates between the drive sheave and a mower deck. The mower deck typically has a driven sheave for each mower blade and various idler and tensioning pulleys as needed to maintain frictional engagement between the driven sheaves and the endless belt. A pair of guide pulleys situated under the drive sheave redirect the endless belt to the mower deck. The guide pulleys rotate on an axis which is normal or almost normal to the vertical, longitudinal plane of the mower vehicle. The orientation of the guide pulleys forces the endless belt to twist through an angle between the drive sheave and guide pulleys which is at or near 90 degrees. Typically, the guide pulleys are located as close as possible to the drive sheave so that the engine may be mounted as low as possible in the mower vehicle to maintain a relatively low center of gravity. Accordingly, the near 90 degree twist angle of the portions of the belt between the drive sheave and the guide pulleys must typically be accomplished over a relatively short distance. A rate of belt twist may be measured in angular degrees per unit length of belt. The rate of belt twist in a typical prior art mule drive may easily exceed 7 degrees per inch between the drive sheave and the guide pulleys. The rate of belt twist of the endless belt between the drive sheave and the guide pulleys limits the size and capacity of the belt as well as reducing the life of the belt.
The limitations inherent in a typical prior art mule drive configuration are three fold. First, in a traditional mule drive arrangement, an engine is positioned in a longitudinal fashion thereby increasing the length and decreasing the maneuverability of the mower vehicle. In a zero turning radius (ZTR) riding lawn mower, the longitudinal orientation of the engine also places the engine further to the rear of the center of rotation for the mower. Because of the need to prevent backward tipping of a ZTR mower about its primary drive wheels, the aft location of the engine forces the designer to position the counter balancing weight of the operator further forward of the center of turn rotation. However, in a ZTR mower, it is preferable to locate the operator close to the center of rotation for turning to reduce the centrifugal force experienced by the operator during tight turns or spin turns. This centrifugal force causes the operator to experience the unwanted sensation of riding at the end of a boom during a tight turn or spin turn. Second, the relative positions of the drive sheave and the guide pulleys are such that the area of the cross section of the belt (or more precisely the width and extent of the central load carrying fibers of the belt) and therefore the power transmission capacity of the belt are limited to allow a 90 degree twist between the drive sheave and a guide pulley. Third, even when the size of the endless belt is properly limited, an endless belt that undergoes repeated abrupt high angle twisting will withstand fewer cycles than a belt which is not subject to such repeated abrupt high angle twisting.